Current dairy evidence

Study summary

The association between cheese consumption and reduced risk of chronic disease is not always accepted by health professionals or consumers, despite the relationship being investigated across numerous epidemiological studies. A new meta-analysis published in the journal, Nutrients therefore investigated the relationship between cheese consumption and all-cause mortality (that is, mortality not attributed to a specific disease).

Results

Nine prospective studies were included in the meta-analysis looking specifically at all-cause mortality (those with a specific disease endpoint were excluded from the review). Studies were published between 1997 and 2015, with a total of 177,655 participants and a mean follow up period between 5-15 years. Over this period, there were a total of 21,365 deaths.

Results showed no significant association between cheese consumption and all-cause mortality. When looking at high versus low cheese consumption, no differences in regards to all-cause mortality were observed. In addition, dose-response analyses (at 43/g cheese per day) also showed no relationship with an increased risk of all-cause mortality.

Implications

The findings of this meta-analysis add to the body of literature showing no consistent association between all-cause, or cause-specific mortality and other dairy foods. It appears that despite the saturated fat and sodium content of cheese, its consumption has a neutral effect when it comes to disease risk. It is likely that multiple nutrients contained within cheese, such as calcium, potassium and magnesium play an important role in its health benefits - as opposed to detrimental effects which is often considered to be the case. In addition, the saturated fat in cheese is composed of over 400 different fatty acids, which each have unique biological significance and potential benefits, highlighting the complexity of the cheese matrix.

Study summary

When an individual shows symptoms of lactose intolerance, dairy is often restricted in the diet, potentially leading to negative health implications later down the track. However, contrary to popular belief, dairy foods do not need to be eliminated from the diet of lactose intolerant individuals. Tolerance can be improved through a variety of measures; one of those being via dietary changes. An example of this is the use of galacto-oligosaccharides (GOS), a prebiotic not digestible by humans, but readily fermented in the gut. It has previously been shown that use of GOS improves lactose digestion and symptoms of lactose intolerance, however not yet been studied are the mechanisms behind these benefits. The aim of this study was to therefore test whether these effects were related to changes in the microbiome of human subjects.

Lactose intolerant subjects (n= 52) were randomised to either a GOS or placebo diet. The amount of GOS increased each day and subjects were asked to avoid dairy foods for the duration of the study. Following completion, subjects were asked to reintroduce dairy into the diet. Fecal samples of were taken at baseline and then at three time periods post treatment; day 0, day 36 and day 66, with changes in the fecal microbiome evaluated.

Results

Key findings were as follows:

After dairy was reintroduced, changes in microbiome composition were observed including increases in the lactose-fermenting species Bifidobacterium, Lactobacillus, and Faecalibacterium; strains which have been associated with beneficial effects throughout the gastrointestinal tract (such as anti-inflammatory properties). Potentially detrimental microbes (such as Enterobacteriaceae) decreased.

These findings correlated with findings from a previous clinical trial by the same research group, which showed an improvement of symptoms (such as abdominal pain) using GOS. For example, the presence of Bifidobacterium was negatively associated with cramping and pain.

Implications

This study highlights the adaptability of the gut microbiome in lactose intolerant individuals, meaning, dairy foods can remain in this diet without the worry for health implications later down the track.

Study summary

The increasing popularity of plant based milk alternatives often means dairy foods are given a bad rap when it comes to health; this is despite their inclusion in evidence based national dietary guidelines, such as the Australian Dietary Guidelines. A recent review therefore aimed to assess the current body of evidence around dairy foods and health.

Using data from meta-analyses, observational studies and randomised controlled trials, the review aimed to answer the following questions; 1/ will a diet that includes dairy lead to better (or worse) health outcomes 2/ should lactose intolerant individuals avoid all dairy foods and 3/ is there scientific evidence to substantiate substituting dairy milk with plant based alternatives.

Results

Based on the author’s review of the literature, answers to the key questions reported in the study summary were as follows:

1/ Will a diet that includes dairy lead to better (or worse) health outcomes?

Based on the totality of evidence, the review showed intake of dairy foods contribute essential nutrients to the diet, and may protect against some of the most prevalent, non-communicable diseases. Some of the key findings included in the review were that that a diet high in dairy lowers the risk of developing type 2 diabetes, while fermented dairy (cheese and yoghurt) may be associated with reduced risk of type 2 diabetes. In regards to CVD, it was shown that 200-300mL of milk per day does not increase risk of CVD, while adequate consumption of dairy is inversely associated with hypertension and stroke. Another positive finding was that dairy consumed as part of an energy restricted diet can help facilitate weight loss.

2/ Should lactose intolerant individuals avoid all dairy foods?

Current research suggests individuals with diagnosed lactose intolerance do not have to cut out dairy from their diet. Cheese has a negligible lactose content, while good bacteria in yoghurt helps facilitate digestion of the lactose.

Despite the increasing market for plant based milk alternatives, few studies have investigated the health effects of replacing cow’s milk with plant based alternatives. However what is currently known is that plant based alternatives are not nutritionally equivalent to cow’s milk (for example, while soy milk is high in protein, it is not high in other dairy essential vitamins and minerals) and as a result, the health effects are presumably different. More research is however needed in this space.

An article in the US based nutrition publication, Today’s Dietitian, discussed the debate around saturated fat and health – in particular, saturated fats and dairy foods. Traditional views around the association between saturated fat and heart disease are now being challenged, with a growing body of evidence showing the health benefits of dairy and it’s role in disease prevention. Read more...

Study summary

Iodine deficiency is a global health issue; the World Health Organisation (WHO) estimates 2.2 million people are iodine deficient. Iodine is particularly important for brain development during early life stages, with even mild deficiency linked to poorer cognitive outcomes in children.

Dairy foods are a natural and important source of iodine, with a cup of milk (250mL) in Australia containing around 57 µg of iodine. Young children require around 90 µg iodine per day and for adults, this requirement increases to around 150 µg per day. A serve of plain milk therefore contributes a significant proportion of iodine to the diet every day.

Milk alternatives have been increasing in popularity, particularly in light of perceived dairy intolerance and avoidance, vegan diets and the proliferation of fad diets. As a result, many are favouring plant based alternatives over cow’s milk; however, this is likely to have substantial impacts on nutrient intakes.

A new US study compared the iodine content of 30 different milk alternatives, and compared this to cow’s milk.

Results

The various milk alternatives analysed as part of this study included soy, almond, coconut, rice, cashew and walnut based beverages. On average, these alternatives contained 3.1 µg of iodine per 250mL, with content ranging from 0.5 – 10.9 µg. On the other hand, cow’s milk contained 96.8 – 101.1 µg, which was significantly higher than the alternatives.

Implications

This study was conducted in the US, and while the iodine content of cow’s milk is notably higher than that of Australian milk (most likely due to differences in animal feed), these findings provide important insights into the nutritional quality of milk alternatives versus cow’s milk. Alternatives vary greatly in their nutrient content and while fortified alternatives may help an individual reach their calcium recommendations, they are not nutritionally equivalent to cow’s milk which contain a number of other essential nutrients, which likely interact in a multitude of ways to influence health. While evidence for the health benefits of alternatives in the diet is lacking, the evidence supporting the health benefits of cow’s milk is much stronger.

Reference

Study summary

In an aim to reduce the risk of heart disease, individuals are often advised by their health professional to switch from regular-fat cheese to reduced-fat cheese. While regular-fat cheese is higher in saturated fat, a growing body of evidence now suggests that the saturated fat in dairy acts differently in the body compared with other sources of dietary fat. Randomised controlled trials show that when compared to butter, cheese does not raise LDL or total cholesterol, however no study has previously compared regular-fat with reduced-fat cheese – until now.

A new randomised controlled trial published in the American Journal of Clinical Nutrition looked at the effect of both varieties of cheese on cholesterol levels and metabolic syndrome risk factors. Danish subjects were randomised to one of three 12-week intervention diets; regular-fat or reduced-fat cheese (approximately 80g per day) or a non-cheese, carbohydrate control. Subjects were asked to live as they normally would, but were asked to replace normal foods in their diet with the test foods. Serum blood lipids and anthropometrics were measured before and after the intervention.

Results

One hundred and thirty-nine participants completed the intervention. Key findings were as follows:

- As expected, intake of fat, including saturated fat was higher in those who consumed regular-fat cheese, compared to reduced-fat cheese and carbohydrate based diets;

- The were no significant changes in weight, fat mass, lean body mass, waist circumference or blood pressure between regular and reduced-fat cheese diets, or between regular-fat or carbohydrate based diets;

- Blood lipid analysis (total, LDL and HDL cholesterol) showed no differences between any of the three intervention diets.

Implications

This study is great news for cheese lovers with findings showing that consumption of regular-fat or reduced-fat cheese has a neutral effect on a number of metabolic syndrome risk factors, including blood cholesterol, helping to dispel popular misconceptions around cheese consumption and heart disease.

Both regular and reduced-fat varieties of cheese are classified as a five food group food and according to the Australian Dietary Guidelines review of the evidence, nutrient dense, high saturated fat foods, like cheese can play an important role in reducing risk of diet related chronic disease. We’re now gaining a much greater understanding of the role of whole foods in healthy dietary patterns, as opposed to isolated nutrients in the diet. It is likely the complex nutrient matrix of five food group foods, including dairy foods, play a role in positive health outcomes.

With nine out of ten Australian’s currently not meeting their recommended intakes from the dairy food group, it is important health professionals continue to advise their patients to enjoy foods in line with the Australian Dietary Guidelines.

Study summary

Appetite has long been of interest when it comes to management of overweight and obesity. Dairy foods may play an important role in this association, potentially via satiety and reducing energy intake at the next meal. However, previous studies have found conflicting results when it comes to the effect of dairy foods on satiety, most likely due to differences in study design across papers. In order to address this, a new meta-analysis collated findings from randomised controlled trials which examined the effects of dairy consumption on various measures of satiety (i.e. hunger, fullness, desire to eat) and food intake at the next meal.

- In studies which looked at second meal intake and in those where a preload was consumed (that is, a test food or beverage prior to meal consumption), there was a decrease in energy consumption (but not when the preload was a fruit drink, cola or chocolate);

- There was a significant increase in energy consumption at the next meal if no preload was consumed.

Implications

Previous meta-analyses have shown dairy foods play a role in weight management and this study sheds light on a possible mechanism underlying these benefits, with findings showing consumption of no less than 500mL of dairy increased feelings of fullness and decreased feelings of hunger which may play a role in energy intake. This is the first systematic review and meta-analysis of randomised controlled trials investigating if dairy foods influence satiety and food intake at the subsequent meal, The Australian Dietary Guidelines recommend adults aged 19-50 years consume 2.5 serves of dairy every day and it’s likely the protein content of dairy – including casein and whey – plays a crucial role in appetite management, and may help with weight management.

Study summary

A healthy diet is important when it comes to stroke prevention and dairy foods have previously been associated with reduced risk of stroke. Previous meta-analyses however, have mostly focused on the association between stroke risk and milk consumption. A more recent systematic review and dose-response meta-analysis published in the Journal of the American Heart Association aimed to re-review the body of evidence, including investigating whether a dose-response relationship exists between dairy food consumption and stroke risk.

Results

Eighteen prospective cohort studies were included in the meta-analysis, comprising over 760,000 participants and just under 30,000 incidents of stroke. The major findings were:

Consumption of 200g/day of milk was associated with a 7% reduced risk of stroke;

Cheese consumption was inversely associated with stroke risk (although marginally), where 40g/day was associated with a 3% lower risk;

Implications

Health professionals may be reluctant to advise consumption of some dairy foods, especially for individuals at risk of stroke, however the findings of this study are in line with others (including the Australian Dietary Guidelines evidence statements) which show an important role for milk and cheese when it comes to stroke prevention. While the mechanisms behind this relationship are not yet fully understood, it is thought that the high calcium content of dairy foods plays an important role, together with other minerals such as potassium and magnesium which are inversely related to stroke risk.

Study summary

Dairy foods are an important source of key nutrients, vitamins and minerals including calcium, protein, phosphorous and riboflavin. Due to their nutrient density, dairy foods are an important contributor to the overall nutritional quality of the diet and may be linked to overall health related quality of life; an important factor when it comes to wellbeing.

A newly published Australian prospective cohort study has investigated whether dairy food consumption could be a marker of a healthy diet, and therefore associated with health related quality of life in adolescents. A sample of 1216 adolescents (mean age 12.7 years) were followed up after a five year period with dairy intake (total intake and intakes of milk, yoghurt and cheese) assessed via a food frequency questionnaire. In addition, quality of life was also assessed using the Pediatric Quality of Life Inventory (PedsQL), which measured physical and psychosocial health, emotional, social and school functioning.

Results

Complete data sets were obtained from 858 participants, who were aged 17 at follow up. A linear relationship was observed between dairy food consumption and scores on the PedsQL. It was also found that when compared to those in the lowest tertile, boys in the highest tertile of yoghurt consumption had higher scores when it came to psychosocial health and school functioning. A similar relationship, however was not observed for girls or for total dairy intake.

Implications

According to the Australian Health Survey, only 2.5% of adolescent boys are currently meeting recommendations for the dairy food group, and are therefore missing out of the health benefits of milk, cheese and yoghurt. This study highlights other important benefits of dairy foods, where daily consumption of dairy, particularly yoghurt could beneficially influence health related quality of life (social, academic or emotional measures) in adolescent boys.

Study summary

The evidence is continuing to grow when it comes to the benefits of dairy foods on weight management. Researchers at CSIRO have collated results from 27 randomised controlled trials looking at the effects of dairy foods (milk, cheese, yoghurt and custard) or dairy protein supplements against a control diet on body weight and body composition. The meta-analysis included 1278 participants aged 18-50 years, with a median study period of 16 weeks.

Results

Compared to a control diet (dairy alternatives, calcium supplements, carbohydrate based controls or lower dairy consumption), consumption of 2-4 serves of dairy foods as part of a calorie controlled diet resulted in:

Implications

This study has shown that increased consumption of dairy contributes to increased weight and fat loss, in overweight and obese women under conditions of energy restriction and builds on previous evidence showing the benefits of milk, yoghurt and cheese when it comes to weight management. While results in this study were strongest for women, most likely due to the lack of studies available in male participants, this work continues to help dispel misconceptions held by some health professionals that milk, cheese and yoghurt may lead to weight gain.